This invention relates to a tone signal synthesizer employing a closed wave guide network and more particularly to such a tone signal synthesizer which is capable of accurately or faithfully simulating tones of natural musical instruments such as natural wind instruments and is also capable of achieving a natural connection of tones.
In sounding tones of desired pitches by a natural wind instrument, the player controls or adjusts the length of the instrument's tubular body (including the opening and closing movement of register keys) and also blow action on the reed section of the mouthpiece (or bite action on the reed).
From the viewpoint of acoustics, to determine the length of the tubular body by, for example, opening and closing the register keys means to determine the resonant frequency in the tubular body. In other words, the tubular body functions as a comb filter with a resonance frequency variably determined from among a given fundamental frequency f and related harmonic frequencies 2f, 3f . . . nf. In response to the player's blow action on the reed section of the mouthpiece, a specific resonance frequency of the tubular body is determined. For explanation, an operation mode of the reed section which causes resonance of the tubular body at the fundamental frequency f will be called a first-order mode, an operation mode which causes resonance at the second-harmonic frequency 2f two times higher than the fundamental will be called a second-order mode, and so on. Namely, an operation mode which causes resonance at the nth harmonic frequency nf n times higher than the fundamental will be called an n-order mode.
By the way, tone waveshape signal forming devices, namely, tone signal synthesizers are conventionally known which simulate the operation of a natural musical instrument such as a wind instrument by the use of electronic circuitry (including software), so as to form tone signals approximating tones of the natural musical instrument. Some of the known tone waveshape signal forming devices employ a closed wave guide network as a tone synthesis means suitable for simulating tones of a wind instrument. The wave guide network comprises a waveshape signal circulation path which is composed of delay circuits and filters connected in a closed loop. An excitation signal is supplied to this circulation path for circulation therethrough, and an output tone signal is taken out from any suitable location along the circulation path. The basic idea of such a wave guide is taught in U.S. Pat. No. 4,984,276.
To describe a case where a wind instrument is simulated, the above-mentioned circulation path corresponds to a tubular body of the wind instrument, and the delay times achieved by delay circuits provided in the circulation path generally corresponds to the length of the tubular body. In some cases, there are also provided circuits corresponding to register keys. Hereinafter, such a circuitry section which makes up the circulation path will be called a "linear section". To this linear section, there are supplied various parameters such as a parameter corresponding to the above-mentioned tubular body length, and a parameter corresponding to the open and closed state of the register keys. The linear section operates in accordance with the supplied parameters, so as to circulate the waveshape signal. The resonance frequency f, 2f, 3f . . . n of the linear section is determined in accordance with the supplied parameters.
A section for generating the excitation signal to be supplied to the linear section corresponds to the reed section (section including the reed) of the wind instrument and will hereinafter be called a "non-linear section". To this non-linear section, there are supplied various parameters such as a parameter corresponding to a breadth pressure applied to the reed section of the wind instrument (pressure parameter), a parameter corresponding to the manner in which the player's mouth contacts the reed section and/or the player bites the reed section (embouchure parameter), and a parameter specifying frequency characteristics of the reed. The non-linear section operates in accordance with the supplied parameters, so as to generate the excitation signal. The operation mode of the non-linear section (which corresponds to the operation mode of the reed section of the wind instrument and will hereinafter be called a "non-linear section operation mode") is determined in accordance with the supplied parameters.
As mentioned above, the tone signal synthesizers employing the wave guide network receives predetermined parameters at the linear section and non-linear section, in such a manner that it operates with the resonance frequency and the non-linear section operation mode as determined by these parameters, thereby simulating a desired natural musical instrument in order to form tone signals of desired pitches.
Improved tone signal synthesizers employing the closed wave guide network are disclosed in U.S. Pat. No. 5,117,729 and in U.S. Pat. No. 5,187,313. According to the disclosure in the first-named U.S. Patent, there is provided a particular signal transfer passage extending from a signal supply line of the network in the linear section to a return signal line. The particular signal transfer passage functions to exchange signals between the two lines in such a manner that it is allowed to simulate characteristics of air flow right behind a gap between the mouthpiece and reed of a natural wind instrument. According to the disclosure in the second-named U.S. Patent, there is provided a signal decay means in a signal junction portion which first processes an excitation signal input from the non-linear section, so as to control a transfer gain of the first-order resonance frequency in so that a resonance frequency of a desired order can be obtained.
However, with the prior art tone signal synthesizer employing the closed wave guide network, no detailed study or consideration was not made on the relationship between the pitch of a tone to be generated and parameters to be supplied to the network for achieving the pitch. Thus, there was no other approach for achieving the pitch than variably controlling only one parameter by, for example, varying the signal delay length in the wave guide. But, such an approach was never sufficient for faithfully simulating tones of a natural musical instrument.